Bismuth phosphovanadate and/or bismuth silicovanadate based yellow pigments and processes of manufacturing thereof

ABSTRACT

A bismuth vanadate based yellow inorganic pigment is disclosed together with a process for making bismuth based yellow inorganic pigments.

OBJECT OF THE INVENTION

The present invention refers to inorganic yellow pigments based onbismuth phosphovanadate and/or silicovanadate as well as processes ofmanufacturing and obtaining said pigments.

Ideally a yellow pigment must have the following characteristics:

1) coloring power, that is, when it is mixed with a large quantity ofwhite pigment, it must hold its own vivid color;

2) intensity, that means it must have a pure color and be exempt ofdullness or greyness;

3) light solidness, that is the color must be maintained when thepigmented object is exposed to light;

4) absence of bleeding, that means no color migration into the pigmentedobject.

Moreover many applications require a great opacifying power of thepigment, that means the capacity of covering and opacifying efficientlythe colored objects.

The main yellow pigments are lead chromates, cadmium sulfides, nickeltitanates, hydrated iron oxides and various organic pigments principallybased on dinitrogenated compounds.

The use of the lead chromates and cadmium sulfides is presently limitedby their possible toxicity; nickel titanates and iron oxides are opaque,but are deficient either in coloring power or in color purity. Theorganic pigments they have generally a low covering power, are expensiveto very expensive and bleed frequently. The bismuth vanadate-basedpigments present a very pure color, great coloring power, a good opacityand no bleeding. The present invention has as an object to provide newpigments based on bismuth phosphovanadate and/or bismuth silicovanadatewhich have all characteristics and qualities of pure bismuth vanadate.

The present invention also refers to new manufacturing processes forbismuth vanadate compounds according to the present invention.

CHARACTERISTIC ELEMENTS OF THE INVENTION

The new yellow inorganic pigments based on bismuth phosphovanadateand/or silicovanadate according to the present invention are non toxicand have a good covering power, a good coloring power, a great colorpurity, a good light solidness and do not bleed in the environmentswhere they are used. Those pigments have the following chemical formula:

    Bi.sub.a L.sub.b M.sub.c N.sub.d O.sub.4

where:

L is Si or simultaneously Si and one or various elements chosen amongstTi, Ge or Zr; or still simultaneously Si and one or various elementschosen amongst Ti, Ge or Zr and one or various elements of the groupIIIa;

M is V or simultaneously V and one or various elements chosen amongstthe group Vb or P;

N is Mo or W;

a varying from 1 to 4/3, and b, c and d varying from 0 to 1;

under the following conditions:

c is higher than 0, and

if b=0 then M must represent simultaneously V and one or variouselements chosen amongst the group Vb or P.

The invention also refers to manufacturing processes for bismuthphosphovanadate and silicovanadate.

According to a preferred embodiment of the invention, a precipitation ofa "raw product" in wet medium is firstly made, then this raw product isconverted into a pigmentary powder through a calcination step in theambient conditions. The precipitation of the raw product is made underwell controlled conditions by mixing an acid solution of bismuth with anaqueous solution containing at least vanadate anions and silicate and/orphosphate anions and possibly molybdate and/or tungstate anions ortitanium, germanium, zirconium, niobium, phosphorus, boron or aluminiumcompounds, preferably titanate, germanate, zirconate, niobate,phosphate, borate, aluminate or silicoborate in presence of a base andat a temperature between 20° and 100° C., preferably between 40° and 80°C. The precipited product is then separated from the mother-waters.These latter are in the case of the invention exempt of heavy metals andother ions such as Bi, Mo, P, Zn, . . . The precipitate is then washedand dried. It is calcinated during 0.5 to 5 hours at a temperature of400° to 700° C.

Nevertheless further embodiments of the process of manufacturing thepigments according to the present invention can be possible.Particularly, solid compounds of bismuth and vanadium, silicon,phosphorus, molybdenum can be intimately mixed and the mixture can bethen directly calcinated. The formation of the bismuth vanadate-basedpigmentary compound is then carried out by chemical reaction in solidphase, as it is also done for the pigments of the rutile and spinellefamily.

Practically there are mixed very intimately oxides or compounds whichare converted into oxides under the action of temperature; into hydratedoxides, hydroxides, carbonates, phosphates, silicates, acetates . . . Tocarry out the mixing, there are used intensives mixers (of blade orploughshare types), breaker mills, turbofeeders, mixers-breakers . . .When the intimate mixing is completely carried out, it is calcinateddirectly in a kiln at temperatures comprised between 400° and 1100° C.during many hours. When calcination is complete, the product is cooledprogressively and there is obtained a yellow product which presentsafter wet grinding, drying and dry grinding the pigmentary properties ofbismuth vanadates.

The treatment can be also made in one step by precipitation in thepresence of catalyst and promoter ions. In that case a bismuth salt isprecipited by vanadate, molybdate, silicate and/or phosphate, borate,aluminate . . . ions. When the reaction is over, the reaction mixture isagain stirred for a more or less long period between 1 and 10 hours attemperatures between 80° and 100° C. or even higher and at a slightlyacid pH between 3 and 7. The humid state aging leads to a yellowcristallized product having the pigmentary characteristics of bismuthvanadates.

SUMMARY OF THE ART

The bismuth vanadate used among others as a yellow pigment forcoloration of plastics and paints or as a catalyst for oxidation ofolefins is a known chemical compound (U.S. Pat. No. 3,843.554, U.S. Pat.No. 4,115,142).

Various processes are described to manufacture pure or complex materialsbased on bismuth vanadate with good pigmentary properties. Generally awet precipitation of the bismuth compound is firstly made by vanadateanions or possibly in presence of molybdate and/or tungstate andpossibly in presence of other cations. Then thermal or chemicaltreatments give the so formed compounds the necessary cristalline andpigmentary properties. Finally various post-treatments can improve theheat resistance in plastics and the light solidness in paints (U.S. Pat.No. 4,063,956, U.S. Pat. No. 4,115,141, U.S. Pat. No. 4,752,460). Alsodry mixing and calcination can be made with no wet calcination step(DE-3 315 850, U.S. Pat. No. 4,251,283 ).

The formation of "multiphase compounds" based on BiVO₄ allows brightyellow pigments to be obtained less expensively than those compoundsbased on the only phase BiVO₄. Thus the simultaneous presence, besidesthe bismuth vanadate, of other compounds such as sulfates, phosphates,oxides, molybdates and tungstates is claimed in various patents : GB-2034 342, DE-3 106 625, DE-3 135 281.

The chemical formula of those multiphase compounds based on bismuthvanadate can be written as follows:

    x BiVO.sub.4.y Bi Me O.sub.4.z ABO.sub.4

Me being generally Mo and/or W ABO₄ being any oxygenated compound.

A multiphase compound based on 2BiVO₄ /BiPO₄ /AlPO₄ is for exampleproduced by calcination of the wet mixture of bismuth phosphate,pentavalent vanadium compounds and trivalent aluminium. The relativeproportions of Al₂ O₃ and P₂ O₅ as well as the calcination temperature(700°-1100° C.) condition the colors obtained which can go from greenishyellow up to orange yellow (DE-2 933 778).

The document JP-63061080 has also made known another bi-phase compoundBiVO₄.xBiPO₄ which is obtained by calcination of a mixture of powderscontaining bismuth, vanadium and phosphorus compounds. That compound isto be used as a temperature reversible indicator material and presentsthat essential characteristic to modify its color depending ontemperature.

Moreover a European patent application published under N° EP-A-0 441 101on Aug. 14, 1991 and claiming a priority of U.S. application Ser. No.463,639 of Jan. 11, 1990 describes pigments based on bismuthphosphovanadate.

DETAILED DESCRIPTION OF THE INVENTION

Yellow pigments with high coloring power based on bismuth phosphateand/or silicate/vanadate can be obtained by mixing and particularly byco-precipitation in absence of fillers and divalent and trivalentcompounds based on Mg, Ca, Ba, Zn, Fe, . . . followed by a calcinationat temperatures lower than 700° C.

The composition of the preferred yellow inorganic pigments according tothe present invention meet to the following chemical formula:

    Bi.sub.4/3-x/3+xy/2 [L.sup.IV.sub.1-x M.sup.V.sub.x-3xy/2 N.sup.VI.sub.xy ]O.sub.4                                                  (formula I)

In that same chemical composition, bismuth is always trivalent, the ionsL, M and N represent respectively tetravalent and/or trivalent,pentavalent and hexavalent ions.

More precisely L represents silicon (and/or titanium, germanium,zirconium, boron or aluminium); the value of [1-x] being generally from0 to 1/8, that means 7/8<x<1.

M is a mixture of vanadium ions and phosphorus and/or niobium ions witha ratio higher than one,

N represents hexavalent molybdenum and/or tungstene; the value of xybeing generally from 0 to 2/3.

For commodity, that formula can be written in a simpler way as follows:

    Bi.sup.III.sub.a L.sup.IV.sub.b M.sup.V.sub.c N.sup.VI.sub.d O.sub.4 (formula II)

where:

a=4/3-x/3+xy/2

b=1-x with 0≦b≦1/8

c=x-3xy/2 with 0<c≦2/3

d=xy with 0≦d≦2/3

For d=0 (and y=0) there will be obtained a bismuthsilico(phosphovanadate); for b and d=0 (x=1 and y=0), there will beobtained a pure phosphovanadate. If d is different from 0, it shouldvary from zero to 2/3 with preferably values from 0.1 to 0.4. As regardsthe phosphorus/vanadium ratio, it can be varied within the followinglimits: ##EQU1##

Preferably the values will be chosen between 1/100 and 1/4.

The pigments according to the present invention are mainly manufacturedwith bismuth vanadate, phosphate, silicate, molybdate and/or tungstate.They are not formed with true solid solutions as it could be deductedfrom above suggested general chemical formula; in reality those pigmentsare highly intimate mixtures of various quite similar phases as theycrystallise in the monoclinic and orthorhombic or cubic systems.

The preparation of the pigments according to a preferred embodiment ofthe invention can be carried out through the following steps: heatco-precipitation of the "raw product", separation of that product byfiltration, careful washing and final calcination to get the pigmentwhich still goes through a wet grinding.

The raw product, which is a mixture of bismuth vanadate, bismuthmolybdate, silicate and/or phosphate and/or other bismuth compounds isobtained preferably by precipitation in an aqueous medium, as there isobtained in that case an extremely intimate mixture of different bismuthcompounds and the stoichimetric composition of the raw product is inthat case perfectly controlled. Consequently the final pigmentaryproduct is perfectly homogenous, the calcination temperature is not veryhigh and it is not necessary to use additives like fluxes. Moreover thewet mixing does not lead to rejection of nocive soluble salts and thereproducibility of the pigmentary characteristics is perfect.

The co-precipitation is made by heat mixing an aqueous solutioncontaining vanadate, molybdate, silicate, phosphate, tungstate, borateand/or aluminate ions with a solution of a bismuth salt. The temperatureof those solutions is adjusted carefully so as to be maintained between20° and 100° C., preferably between 40° and 80° C. The solutions can beadded to each other either successively or simultaneously.

If the procedure is successive, the process consists in pouring on a nonhydrolyzed acid solution of a bismuth salt a mixture of vanadate and/orsilicate or phosphate, molybdate, . . . during 0.25 to 3 hours,generally between 0.75 and 1.5 hours. While adding the solutions, itwill be taken care that the stirring is efficient and the temperaturemaintained between 40° and 80° C. The pH of the reaction mixture goes upgradually from zero or less to a value near one. Then by dripping analkaline solution the pH is increased up to a value from 2 to 6,preferably from 3.5 to 4.5.

If the procedure is simultaneous, the process consists in pouringtogether in a reactor equipped with a highly efficient stirrer the hotsolution of bismuth and the hot solution comprising the anions; theoperation is preferably made with an advance of 1 to 10% of the bismuthsolution. The pouring time of the solutions is from 0.5 to 2 hours,preferably 0.75 to 1.5 hours. During the whole pouring time, care istaken that the temperature of the reaction mixture is maintained between40° and 80° C. Afterwards stirring is still continued for an intervalbetween 0 and 2 hours, preferably between 10 and 30 minutes. The pH,which is near one, is then brought gradually up to a value between 2 and6, preferably between 3.5 and 4.5 by addition of a concentrated basesuch as caustic soda, sodium carbonate, potassium hydroxide or ammoniasolution.

In such a way a not very cristalline compound of creamy yellow color isprecipited, which is a highly intimate mixture of the components of thefinal pigment. Before separating that raw product from themother-waters, it can be left to mature for 0.5 to 5 hours in order tomake the precipitation totally completed. Consequently every trace ofheavy metal ions or other requiring expensive purifications can beeliminated from the mother-waters. The product obtained is thenfiltrated and separated from the mother-waters; the paste produced isthen washed with water and dried.

The calcination is used to convert the raw product which is in a more orless amorphous condition into a crystalline pigment with a beautifulpure yellow color. That thermal treatment or calcination is carried outin presence of air in a kiln at a temperature varying between 400° and700° C., preferably between 550° and 625° C. If lower temperatures areused, the product will not be converted into an homogenous cristallinecompound and the color will remain quite dull. If the workingtemperatures are too high, there is a risk to obtain a very hard productwith a dirty deep color.

Calcination is carried out in an electrically-heated kiln of tunnelfurnace type, muffle furnace type or even rotating furnace whichguarantee an excellent homogeneity and allow a continuous and constantproduction. The calcination time varies between 0.5 and 5 hours.Calcination is carried out in an oxidative environment either in theambiant air or with compressed air or with a mixture of air and oxygen.

After the calcination, the pigment is progressively cooled. Neverthelessthe preparation process according to the present invention makespossible to cool the pigment rapidly. In less than one hour thetemperature can be decreased 150° C. and even more without altering thecoloristic and pigmentary characteristics.

Finally the calcined pigment is ground in a wet medium with ball mills,sand mills, microball mills, . . . With such a wet grinding (contrary toa more conventional dry grinding) a pigment can be obtained with a verypure color and a very fine texture. After that wet grinding the productis filtrated, dried and finally ground conventionally.

As a trivalent bismuth salt there can be used bismuth nitrate, bismuthcarbonate, bismuth acetate and any other aqueous solution of those saltssufficiently acidified so as not to be hydrolyzed. Generally an aqueoussolution of bismuth nitrate Bi(NO₃)₃.5H₂ O in nitric acid is used.

As a vanadium source there can be used the pentavalent combinations suchas V₂ O₅, Na₃ VO₄, Na VO₃, NH₄ VO₃. The alkaline metavanadates arepreferred.

As a source of molybdenum and/or tungsten, sodium molybdate andtungstate Na₂ MoO₄.2H₂ O and Na₂ WO₄.2H₂ O can be used particularly.

As a source of phosphorus, 85% phosphoric acid H₃ PO₄ as such or analkaline phosphate can be used.

As a source of silicon there can be used anhydrous sodium metasilicate,liquid sodium silicates, liquid potassium silicates, powdered potassiumsilicate or any other silicon-based compounds (for example silanes).

As a source of aluminium, there can be used aluminates of alkalinemetals; as a source of boron, there can be used ammonium, potassium orsodium metaborates and tetraborates as well as boric acid H₃ BO₃.

During or after the wet grinding, the pigment can still go through asurface treatment so as to improve its heat and light resistances. Thepigment is covered with a coating--which can also be precipited on itssurface--based on well known inorganic or organic compounds: the oxides,hydrates, phosphates, esters, carbonates, silicates of titanium,aluminium, antimony, zirconium, hafnium, boron, rare earths, silicon,calcium, barium magnesium and strontium are currently used.

The so obtained pigments are particularly convenient to dye plastics andindustrial paints.

With respect to other manufacturing processes such as dry or wet mixingof powders, direct calcination, precipitation followed by an agingwithout calcination, the advantages of this two step method, that meansa co-precipitation followed by an oxydative calcination are significant:

the co-precipitation assures a perfect mixing of the pigment componentswhich are formed simultaneously in situ

the calcination temperature can so be adjusted very finely and is thusless high. It is also possible to work without any flux or otheradditive.

the calcination time is reduced; generally 1 hour is sufficient

the co-precipitation reaction is a chemical reaction with a yield of100%;

the mother-waters are thus exempt of ions such as bismuth, vanadate,molybdate, phosphate, zinc, . . . and polluted and/or uneasilypurifiable rejections can be avoided. Particularly the presence ofsilicate as well as aluminate or borate makes possible a stoichiometricprecipitation which is not easily obtained or with high difficulty inpresence of other anions of phosphate, fluoride, . . . types.

that process of manufacturing makes possible to obtain a pigment ofbismuth vanadate with a high purity and a high coloring power, althoughit contains a large quantity of molybdate; thus the ratio Mo/V estcomprised between 0.5 and 0.75 with extremes comprised between 0.4 and0.85, whereas according to other conventional processes (dry mixing,direct calcination, precipitation without calcination), the ration Mo/Vmust be comprised in a range of 0 to 0.25 in order to obtain the samequalities in terms of color and coloring power. According to the processof the present invention, a pigment of excellent quality is obtained fora well lower cost of raw materials.

Nevertheless the most conventional processes of preparation of pigmentsaccording to the present invention also lead to good results.Particularly there can be mentioned processes of direct calcination orprecipitation with crystalline aging without further calcination.

In the case of direct calcination, a bismuth compound is mixed veryintensively with vanadium, molybdenum, tungsten, silicon, . . . in amechanic mortar or in a mixer-breaker. As bismuth compounds, there canbe used neutral or basic nitrate, trioxide, phosphate, subcarbonate,basic acetate or any other bismuth compound which is able to beconverted into oxide under temperature action. For the other components,namely molybdate, vanadate, silicate, phosphate, tungstate, aluminate,borate, . . . any combination which can produce an oxide or anoxygenated ion in the calcination step can be used.

For example, an intimate mixture can be made in an intensive mixer ofbismuth oxide Bi₂ O₃ with conveniently dosed quantities of vanadiumpentoxide V₂ O₅, sodium metasilicate Na₂ SiO₃ and molybdenum oxide MoO₃,the case being one of those compounds can be totally or partiallysubstituted by sodium aluminate, bismuth phosphate, talc, boron oxide,tungsten trioxide or any other low solubility oxygenated compound basedon silicon, vanadium, phosphorus, boron, aluminium, . . .

The mixing can also be carried out by intimate dispersion of the variouscomponents in a turbine under strong agitation in an aqueous medium;this mixture is then dried at a temperature of about 100°-130° C. andfinally ground in a mortar and calcinated according to the conditionsdescribed in those processes.

The mixture is calcinated in a kiln during 1 to 50 hours, preferablyduring a time of 3 to 8 hours at temperatures comprised between 400° and1100° C., and preferably between 650° and 850° C. The optimumtemperature depends on the relative composition of the mixture to becalcinated. High temperatures assure a quicker solid phase reaction, butbeyond a certain temperature, the mixture melts and gives a hard andless pigmentary mass. In the presence of tungsten, the limit meltingtemperature is higher than with molybdenum or boric acid. Generallytemperatures near 750° C. will be preferably chosen. Calcination timecan vary from 1 to 50 hours; however it will be longer for lowtemperatures than for high temperatures. With temperature valuescomprised between 700° and 800° C., calcination takes usually timescomprised between 3 and 8 hours. It is sometimes interesting to shortenthe calcination time by calcinating in a first step at 650° C., thengrinding the calcinated product and calcinating it again in a secondstep at 750°-800° C.

The calcinated product is slowly cooled and then ground in a wet mediumin a ball mill. This grinding allows, contrary to a possible drygrinding, a pigment of pure color the particles of which have normalpigmentary dimensions of the order of one micron, to be obtained. Afterthe wet grinding, the obtained product is washed, dried and dry ground.

The following examples are given to illustrate the present invention.

Control example 1 (bismuth molybdovanadate)

A control sample is prepared by the following procedure:

An acid solution of 107.7 g of bismuth nitrate (specific weight 1.607g/cm³) is poured in a 5 l reactor. The volume is adjusted to 0.570 l byadding hot water and the temperature is adjusted to 70° C.

Under agitation an addition is made of an aqueous solution containing14.779 g sodium vanadate and 18.333 g sodium molybdate in 3.6 l water.The addition is made in 2 hours. During that addition the pH of thereaction mixture goes up gradually up to 0.5; it is then adjusted to 4.5by drop addition of 63 ml of 50% caustic soda. After a further agitationof one hour at a temperature of 70° C., the pH is stabilized at 3.8. Themixture is then filtered, washed with water and dried during 12 hours at90° C. There are obtained 85.5 g raw product which are then calcinatedduring 1 hour at 620° C. The yellow pigment obtained is ground in apearl mill. After filtration, drying and grinding, a pigmentary powderis obtained with the following composition:

    Bi.sub.1.160 V.sub.0.520.sup.Mo.sub.0.320 O.sub.4

(x=1, y=0.32)

That pigment forms a good control standard for the other examples.

Control example 2 (pure bismuth vanadate)

A sample of pure bismuth vanadate is prepared according to the procedureof example 1, except that the sodium molybdate is omitted: to 48.98 gbismuth nitrate are added 15.12 g sodium metavanadate. A yellow pigmentis then obtained with the following composition:

    Bi.sub.1.000 V.sub.1.000 O.sub.4

(x=1, y=0) the color of which can be compared to reference one.

Example 3 (bismuth silicovanadate)

According to the procedure described in example 1, a bismuthsilicovanadate is prepared by mixing 102.240 g bismuth nitrate, 28.700 gsodium vanadate and 3.750 g sodium metasilicate. A bright yellow pigmentis obtained of the following composition:

    Bi.sub.1.023 Si.sub.0.070 V.sub.0.930 O.sub.4

(x=0.93, y=0)

the coloring power and opacity of which are well higher than those ofthe pure bismuth vanadate of example 2.

Example 4 (bismuth silicomolybdovanadate)

54.250 g bismuth nitrate [acid solution containing 22.6% Bi(NO₃)₃ ] arepoured in a 3 l receptacle. Volume is adjusted to 0.285 l by addingwater and temperature is brought to 70° C. To that solution of nonhydrolyzed bismuth nitrate is added in one hour a solution of 6.510 gsodium vanadate NaVO₃, 9.700 g sodium molybdate Na₂ MoO₄.2H₂ O and 0.650g sodium metasilicate Na₂ SiO₃.5H₂ O in 1.8 l water at 70° C. After thataddition, pH is adjusted to a value of 2 by addition of caustic soda inconcentrated aqueous solution. Agitation is continued for 2 hours whilemaintaining temperature at 70° C. Then the product is filtrated bysuction, washed carefully with water and dried in an aerated stove at85° C. during 12 hours. The raw pigment is then reduced into a powderand calcinated during 90 minutes at 625° C. 43 g of pure yellow pigmentare thus obtained which are ground finely in an aqueous medium in apearl-mill. Finally after filtration, drying and grinding a yellowpigmentary powder is obtained with the following composition:

    Bi.sub.1.181 Si.sub.0.0026 V.sub.0.458 Mo.sub.0.344 O.sub.4

(x=0.974, y=0.353)

the coloring power of which is higher than the control one of example 1.

Example 5 (bismuth silicomolybdovanadate)

According to the procedure described in example 1, a bismuthsilicomolybdovanadate is prepared by adding 53.325 g bismuth nitrate,6.10 g sodium metavanadate, 9.075 g sodium molybdate and 1.7 g sodiummetasilicate Na₂ SiO₃.5H₂ O. Consequently a bright light yellow pigmentis obtained with the following composition:

    Bi.sub.1.187 Si.sub.0.066 V.sub.0.441 Mo.sub.0.329 O.sub.4

(x=0.934, y=0.352)

the coloring power of which is higher than the control one (20-25%).

Example 6 (bismuth silicomolybdovanadate)

According to the procedure described in example 1, a mixture is preparedwith 55.3 g bismuth nitrate, 4.68 g ammonium vanadate, 7.26 g sodiummolybdate and 7.15 g sodium silicate (25.2% .SiO₂ solution). A yellowpigment is obtained with the following composition:

    Bi.sub.1.217 Si.sub.0.261 V.sub.0.348 Mo.sub.0.261 O.sub.4

(x=0.739, y=0.353)

the coloring power of which is not higher than the control one ofexample 1 because of the silicate excess.

Example 7 (bismuth phosphovanadate)

50.659 g bismuth nitrate (acid solution of pH=0 containing 22.6 weight %bismuth) are poured in a 3 l receptacle.

Volume is adjusted to 0.25 l by water addition and temperature isbrought to 75° C.

In one hour that non hydrolyzed solution of bismuth nitrate is addedwith a solution of 6.585 g sodium vanadate NaVO₃, 8.167 g sodiummolybdate and 0.602 g 100% phosphoric acid in 1.6 l water at 80° C.

After that addition, pH is adjusted to 2 by adding caustic soda in aconcentrated aqueous solution.

Agitation of the pigment is continued during 2 hours while maintainingthe temperature between 70° and 80° C. Then filtration is carried out bysuction, the product is carefully washed with water and dried in anaerated stove at 80° C. during 12 hours. The raw pigment is then reducedinto powder and calcinated during 1.30 hours at 620° C. In such a way 40g pure yellow pigment are obtained which are finely ground in an aqueousmedium in a pearl-mill. Finally after filtration, drying and grinding, ayellow pigmentary powder is obtained with the following composition:

    Bi.sub.1.152 V.sub.0.485 P.sub.0.061 Mo.sub.0.303 O.sub.4

(x=1, y=0.303, P/V=0.126)

Example 8 (bismuth phosphomolybdovanadate)

According to the procedure described in examples 1 and 2, a bismuthphosphomolybdodovanadate is prepared by mixing 52.14 g Bi(NO₃)₂, 5.85 gNaVO₃, 8.712 g sodium molybdate and 1.390 g phosphoric acid. Finally alight yellow pigment is obtained with the following composition:

    Bi.sub.1.158 V.sub.0.421 P.sub.0.105 Mo.sub.0.316 O.sub.4

(x=1, y=0.316, P/V=0.25)

the color of which is comparable to the control and the coloring power7% higher.

Example 9 (bismuth phosphomolybdovanadate)

According to the procedure described in examples 1 and 2, a bismuthphosphomolybdovanadate is prepared by mixing 50.030 g bismuth nitrate,6.07 g sodium metavanadate, 8.903 g sodium molybdate and 0.650 gphosphoric acid. Finally a bright light yellow pigment is obtained withthe following composition:

    Bi.sub.1.167 V.sub.0.450 P.sub.0.050 Mo.sub.0.333 O.sub.4

(x=1, y=0.333, P/V=0.111)

the coloring power of which is higher than the control one (20%)

Example 10 (bismuth silicoborovanadate)

According to the procedure described in example 1, a bismuthsilicovanadate is prepared in which a part of silicon is substituted byboron by mixing:

99.225 g bismuth nitrate Bi(NO₃)₃.5H₂ O

9.120 g ammonium metavanadate NH₄ VO₃

14.142 g sodium molybdate Na₂ MoO₄.2H₂ O

0.375 g boric acide H₃ BO₃

1.425 g Sodium silicate in a 25.8% SiO₂ solution

There is obtained a light yellow pigment corresponding perfectly toexamples 4 and 5 in color as well as in coloring power.

Example 11 (bismuth phosphosilicovanadate )

According to the procedure described in example 1, a bismuthsilicovanadate is prepared where a part of the vanadium is substitutedby phosphorus, by mixing a solution of 104.260 g bismuth nitrate and anaqueous solution containing 12.175 g sodium vanadate, 1.790 g sodiummetasilicate, 17.975 g sodium molybdate and 0.645 85% phosphoric acid. Ayellow pigmentary powder is obtained with the following composition:

    Bi.sub.1.176 Si.sub.0.066 V.sub.0.431 P.sub.0.105 Mo.sub.0.323 O.sub.4

the coloring power of which is higher than the control one.

Example 12 (co-precipitation by simultaneous pourings)

2 × the quantities of the products of example 5 are used, but bothsolutions are added simultaneously in a 5 l reactor under strongagitation. Practically, firstly 30 ml of the acid solution of bismuthnitrate are poured, then both solutions are pumped simultaneously, thefirst one at a rate of 9 ml/min, the second one at a rate of 60 ml/min.The temperature of the reactor and its contents is maintained constantat 75° C. When both solutions are poured, they are stirred again 20minutes, and then pH is brought from 1 to 4 by drop addition of 100 mlcaustic soda at 30% The mixture is then filtrated, washed, dried andcalcinated and treated as in example 1. A bright yellow pigmentay powderis obtained exactly similar to the product of example 5.

Example 13

In a small bladed mixer, 445 g basic bismuth carbonate, 52.5 g vanadiumoxide, 6.5 g sodium metasilicate and 58 g molybdenum trioxide are mixedvery intimately. This mixture is then poured in porcelain crucibleswhich are put in a muffle furnace. Calcination is carried out during 5hours at 725° C. The calcinated product is then slowly cooled. Thefragments are ground in an aqueous medium in a pearl-mill during 45minutes. After filtration, washing, drying at 120° C. and dry grinding,a yellow pigmentary powder is obtained similar to the product of example4.

The pigments obtained according to the present invention have excellentproperties for coloration of paints and thermoplastics. Compared to thecontrol pigment (example 1), the pigments obtained have higher purity,covering power and coloring power.

To compare the heat stability, the pigments according the presentinvention and the control pigments are each mixed with a plastics(PE.PP). The granules obtained are then extruded at differenttemperatures during 5 minutes.

To compare light solidness, the pigments according to the presentinvention and the control pigments are incorporated each into a paintthe various samples of which are exposed to light (QV) and weatheringagents.

    ______________________________________                                                   Colour      Colouring power                                        ______________________________________                                        Example 1                  100                                                control                                                                       Bi (V, Mo) O.sub.4                                                            Example 2    orange yellow 100                                                Bi V O.sub.4                                                                  Example 3    light yellow  110                                                Bi (Si V) O.sub.4                                                             Examples 4 and 13                                                                          light yellow  115                                                Bi (Si V Mo) O.sub.4                                                          Examples 5 and 12                                                                          light yellow  125                                                Bi (Si V Mo) O.sub.4                                                          Example 6    light yellow  100                                                Bi (Si V Mo) O.sub.4                                                          Example 7    bright yellow 112                                                Bi (V, P) Mo O.sub.4                                                          Example 8    light yellow  105                                                Bi (V, P) Mo O.sub.4                                                          Example 9    light yellow  123                                                Bi (V, P) Mo O.sub.4                                                          Example 10   light yellow  115                                                Bi (Si B V Mo) O.sub.4                                                        Example 11   light yellow  115                                                Bi (Si V P MO) O.sub.4                                                        ______________________________________                                    

It can be seen clearly that in the compounds of formula I where 1-x iscomprised between 0 and 1/8, the addition of bismuth phosphate and/orbismuth silicate improves the quality of the pigment obtained: brightpure color and better coloring power.

In the annexed figures, the results have been represented under the formof spectral curves of two controls, two silicovanadates, onephosphovanadate as well as measurements of the coloring power of twosilicovanadates compared to their control (FIGS. 1 to 7).

We claim:
 1. A bismuth-vanadate-based yellow inorganic pigment, havingthe formula:

    Bi.sub.a L.sub.b M.sub.c N.sub.d O.sub.4

where: L is selected from the group consisting of Si, andthe combinationof Si and one or more of the elements selected from the group consistingof Ti, Oe, and Zr, and the combination of Si, one or more of theelements selected from the group consisting of Ti, Ge, and Zr, and oneor more of the elements selected from the group consisting of B, Al, Oa,In and Tl; M is selected from the group consisting of V, andthecombination of V and one or more of the elements selected from the groupconsisting of V, Nb, Ta, Unp and P; N is an element selected from thegroup consisting of Mo and W; ≦ a≦4/3; 0≦b<1; 0<c≦1; and 0≦d<1;providedthat if c is greater than zero and b is equal to zero then M is V andone or more of the elements selected from the group consisting of V, Nb,Ta, Unp and P; further provided that if b and d are equal to zero then Mdoes not include P.
 2. The pigment of claim 1 having the formula:

    Bi.sub.4/3-X/3+xy/2 [L.sup.IV.sub.1-x M.sup.V.sub.x-3xy/2 N.sup.VI.sub.xy ]O.sub.4

where: Bi is a trivalent ion; L is one or more of the ions selected fromthe group consisting of tetravalent ions and trivalent ions "of theelements Si, Ti, Ge, Zr, B, Al, Ga, In and Tl"; M is a pentavalent ionmixture of vanadium ions and one or more ions selected from the groupconsisting of phosphorus ions and ions of V, Nb, Ta and Unp; providedthat the ratio of vanadium ions to the other ions in the mixture isgreater than or equal to one; N is a hexavalent ion of an elementselected from the group consisting of molybdenum and tungsten;0<1-x<1/8;and 0<xy<2/3.
 3. The pigment of claim 1 wherein d has a value between 0and 2/3.
 4. The pigment of claim 1 wherein the ratio of vanadium tophosphorus is between 4 and
 100. 5. A process of manufacturing abismuth-vanadate-based yellow inorganic pigment comprising the stepsof:(a) mixing an acid solution of bismuth nitrate with an aqueoussolution of vanadate ions and one or more aqueous solutions selectedfrom the group consisting of aqueous solutions of phosphate ions,silicate ions, molybdate ions, tungstate ions, Ti salts, Ge salts, Zrsalts and Nb salts to form a precipitate and mother-waters; (b)separating the precipitate from the mother-waters; (c) washing theprecipitate; and, (d) calcining the precipitate at a temperature of 400°to 700° C. for 0.5 to 5 hours to form a calcinated pigment.
 6. Theprocess of claim 5 wherein the ratio of phosphate ions to vanadate ionsis greater than or equal to 0 and less than or equal to
 1. 7. Theprocess of claim 5 wherein the ratio of silicate ions to ions of thegroup consisting of B, Al, Ga, In and Tl is between 0 and
 1. 8. Theprocess of claim 5 further comprising the step of maintaining thesolutions at a temperature ranging from about 20° to about 100° C. 9.The process of claim 8 wherein the acidity of the solution is reduced bythe addition of base.
 10. The process of claim 9 where the basecomprises one or more bases selected from the group consisting ofcaustic soda, sodium carbonate, potassium hydroxide and ammonia water.11. The process of claim 5 further comprising the step of maintainingthe solutions of a temperature ranging from about 40° to about 80° C.12. The process of claim 5 wherein the precipitate is aged for 0.5 to 5hours before it is separated from the mother-waters.
 13. The process ofclaim 8, further comprising the steps of:(a) cooling the calcinatedpigment in a wet environment; and, (b) grinding the calcinated pigmentin a wet environment.
 14. The process of claim 13, further comprisingthe step of subjecting the calcineted pigment to a surface treatment toimprove the pigment's heat and light resistances, the surface treatmentcomprising the step of coating the pigment with a compound selected fromthe group consisting of oxides, hydrates, phosphates, esters,carbonates, titanium silicate, aluminum, antimony, zircon/urn, hafnium,boron, silicon, magnesium, calcium, barium, strontium, La, Ce, Pr, Nd,Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.
 15. The process of claim14, further comprising the steps of:(a) filtering the calcinated pigmentto form a filtered pigment; (b) washing the filtered pigment to form awashed pigment; (c) drying the washed pigment to form a dried pigment;and, (d) reducing the dried pigment to powder.
 16. The process of claim14 wherein the step of coating the pigment is accomplished byprecipitating a coating onto the pigment's surface.
 17. A process ofmanufacturing a bismuth-vanadate-based yellow inorganic pigmentcomprising the steps of:(a) mixing powders of bismuth compounds,vanadium ions and one or more ions selected from the group consisting ofthe ions of silicon and phosphorus, and (b) calcining the resultingmixture at a temperature ranging from about 400° to about 1100° C. for aperiod of time ranging from about 1 to about 50 hours.
 18. The processof claim 17 wherein the step of mixing includes mixing powders ofbismuth compounds and powders of one or more ions selected from thegroup consisting of molybdenum, tungsten, titanium, germanium,zirconium, niobium, aluminum, and boron ions.
 19. In a method forcoloring plastic or industrial paint, the improvement comprising usingthe pigment of claim 1 as a colorant.